Coupling between nonparallel waveguides is studied by coupling mode theory, and the coupling equations and coupling coefficients are obtained. Using small angle approximation, results under several conditions are obtained,which are then compared with that of another method. Although both methods indicate that the optical power approaches to a stable value at positions far from the input,yet the values of optical power obtained by them are quite different. To be specific, near the input, optical power changes more violently with propagation distance for the method used by us. Since the effects of both optical amplitude and phase on the coupling equations and coupling coefficients are considered fully in the present method, our results are more comprehensive in describing the coupling of nonparallel waveguides and should be more meaningful for practical applications.